Radar speed is not used at all. The times are based on your estimate for the feeder fix calculated via you flight plan TAS and the forecast winds. That 3 minutes you talk of will shunt you back.
I note Virgin aircraft plan an economy cruise often but don't actually fly that slow (around a 380 TAS). Even though you may really be doing 440 TAS, unless you tell us and we change the flight plan, Maestro will calculate you order in the sequence using the actual TAS in the flight plan and you will find yourself being pushed back down the line.
Times when you are being sequenced with aircraft around you, it is obvious when the TAS is wrong but if you are following a stream from the other direction, you will just have no chance of us picking it up.
Additionally for Eastern Dash 8 types, when you change aircraft and the change is to get a 200 or 300 when initially flight planned as a 100 series, your company usually changes the rego and type but not the TAS resulting in your TAS being 240 as opposed to the usual 270 for the other types. This often costs you slots as well. We have no need to check it and coming into Sydney from the north it is not obvious as usually some are from the north west and others from the north east and with the prevailing wind, your groundspeed wont give it away unless you are following directly in trail.
All of this said, we as do physically update the feeder fix time using the ground speed but in a full runway situation a wrong TAS will still cost you when you are dead heating with 1 or more aircraft.